The book takes a deep dive into the relationship between Simpson, 39, and Mayer, detailing her insecurities in the relationship and the infamous 2010 Playboy interview in which Mayer referred to Simpson as "sexual napalm."

Speaking to Cohen, 51, Mayer said: "As Pee-wee Herman says in Pee-wee's Big Adventure before the movie of his life is about to play out at the end, he's not watching the movie, and the reason he's not watching the movie, he says, 'I don't have to watch it, Dottie, I lived it.' And I think that's prescient here."

In January, Simpson told People magazine that she was "floored and embarrassed" by Mayer's comments to Playboy.

"A woman and how they are in bed is not something that is ever talked about," she said. "It was shocking."

Simpson said she found his comments to be out of character but ultimately very telling.

Jessica Simpson’s tell-all memoir spilt details of her relationships with famous exes, including Mayer. Picture: Supplied.

"He was the most loyal person on the planet and when I read that he wasn't, that was it for me," she said. "I erased his number. He made it easy for me to walk away."

Mayer told TheNew York Times in 2017 that his comments were "far out of touch."

In Open Book, Simpson reveals that her therapist made her realise Mayer never loved her - he was just obsessed with her.

"Ooh, that broke me in half!" she told the New York Times this year of the epiphany. "And that's years into being married and having kids. And it was like, 'Wow. I did this all for obsession? This was his way of loving me?' I think that it just never clicked until it was just blatantly said to me: That's not love."

Simpson said Mayer didn’t really love her – he was just ‘obsessed’ with her. Picture: Supplied.

Simpson revealed in the same interview that she didn't tell him about the memoir despite the fact that he appears in it frequently.